This invention relates to the sharpening of rotary metal-cutting tools known as end mills, and more particularly concerns apparatus for sharpening the face cutting edges of end mills to produce critically defined primary and secondary clearance angles and dish angle.
Milling tools are extensively used for the machining of metal structures to desired shapes. The milling tool, generally fabricated of special alloy steel having a very high hardness, is an integral monolithic structure comprised of a spindle or shaft portion and a cutting head portion disposed at an extremity of said shaft portion and coaxial therewith. The cutting head is comprised of a core which is substantially a continuation of the shaft, and a number of flutes upraised from the core, the outermost extremities of said flutes having elongated cutting edges in parallel juxtaposition symmetrically disposed about the tool axis. The cutting edges of the flutes, generally referred to as the side or axial cutting edges are disposed in a circular cylindrical locus about the tool axis, said edges being either straight and parallel to the axis, or helically disposed to the axis. The diameter of the cylindrical perimeter of the cutting head will generally range from about 0.125" to 4.0".
The cutting head terminates at the end of the milling tool substantially in a plane perpendicular to the axis, said plane being generally referred to as the cutting face and provided with cutting edges substantially radially oriented with respect to the axis. Each face cutting edge is associated with a side cutting edge in a manner such that the extremities of said edges meet at sites defining a circle centered on the axis and perpendicular thereto, said circle lying in a plane which may be considered the effective plane of the cutting face.
When the end mill is rotated about its axis and forcibly applied against a workpiece, the face cutting edges will cut metal from a surface of the workpiece in planes parallel to the cutting face. The side cutting edges of the end mill permit cutting of metal in directions transverse to the rotational axis. By such mode of function, the milling tool is capable of operating in three dimensions upon the workpiece.
The face cutting edges are straight edges which are angled with respect to the plane of the cutting face such that the innermost extremity of the edge is displaced from said plane in the direction of the spindle. The angle between the face cutting edge and the plane of the cutting face is generally referred to as the base cutting edge angle or "dish" angle and usually has a value between 0.degree. and 3.degree..
Each face cutting edge is comprised of a leading surface and a trailing surface. The leading surface is disposed in a plane which is parallel to the tool axis in the case of straight flutes, and angled to the axis in the case of helical flutes. The trailing surface forms an angle of between 4.degree. and 12.degree. with respect to the plane or conical surface containing all the face cutting edges, said angle generally being referred to as the primary clearance angle and being approximately the same as the angle between the trailing surface and plane of the cutting face. The trailing surface is generally provided with a chamfer in a zone spaced away from the cutting edge. The purpose of the chamfer is to facilitate removal of metal chips and thereby reduce wear of the tool. The zone of the trailing surface between the cutting edge and the beginning of the chamfer is referred to as the land. The angle between the chamfer and the plane of the cutting face is generally 10.degree. greater than the primary clearance angle, and this is generally referred to as the secondary clearance angle.
After prolonged use, the cutting edges of the end mill must be sharpened. The sharpening technique requires high precision in order to maintain the proper critical dimensional characteristics of the cutting edges. Sharpening is generally accomplished by contacting the trailing surfaces of the cutting edges with a rapidly rotating abrasive wheel comprised of a composition containing alundum, carborundum, diamond or other materials having a hardness above 9.0 on the original Mohs Hardness Scale. In order to secure accurate and uniform cutting edge angles, special holding and guiding equipment is required to precisely present the cutting edges to the abrasive wheel. Such equipment heretofore available for the precision sharpening of milling tools has required time-consuming manipulations, repeated adjustments and re-mountings of the milling tool to secure the sought cutting edge angles and to compensate for factors such as the diameter and configuration of the cutting head.
For example, in U.S. Pat. No. 4,134,235 to Maharidge, repeated tilting adjustments must be made in the apparatus that holds the milling tool in order to secure the appropriate dish angle on each edge. Such repeated manipulations of the sharpening apparatus not only prolong the time needed for the sharpening operation, but increase the risk of operator errors.
It is accordingly an object of the present invention to provide apparatus for the precision rapid sharpening of the face cutting edges of an end mill.
It is another object of the present invention to provide apparatus as in the foregoing objective which grinds the trailing surfaces of said edges to establish proper primary and secondary clearance angles.
It is a further object of the invention to provide apparatus of the aforesaid nature which additionally establishes a proper base cutting edge angle or dish angle of said cutting edges.
It is still another object of the present invention to provide apparatus of the aforesaid nature which, with a single mounting of a milling tool, will accomplish the aforesaid objectives.
These objects and other objects and advantages of the invention will be apparent from the following description.